1. Field of the Invention
The present invention relates to a photographing apparatus, more specifically, to a controller for auto-focus in the photographing apparatus such as a digital camera or the like.
2. Description of the Prior Art
AF (Auto-focus) is required to operate as fast as possible in a photographing apparatus (hereinafter simply referred to as a “camera”) such as a digital camera or the like.
Conventionally, in AF technique of cameras utilizing a charge coupled device (CCD), a circuit for obtaining values for evaluating the AF is disposed in the preceding stage of an edge emphasizing section of a signal circuit, and thus the integral of a high frequency component of image data itself determined by a subject and a photographing optical system is used as an AF evaluating value. AF processing is performed in such a manner that the AF evaluating value is maximized. Generally, in this case, an entire lens- moving area covering from the closest range photographable (hereinafter simply referred to as a “close position”) to an infinite distance (hereinafter simply referred to as a “infinity”) is checked and roughly adjusted at predetermined intervals to search for a vicinity of a focus position. Further, this limited area or vicinity is subjected to fine adjustment, thereby obtaining focusing.
This type of conventional AF has the following disadvantages.
That is, the conventional type of AF takes a relatively long time to perform the auto-focusing in use.
Further, in the case of photographing a subject having brightness lower than a predetermined limit, output of the CCD becomes so small that dark current noise, which is called random noise in general, is remarkably increased.
Under these conditions, distribution of an AF evaluating value for the focus position is complicated and has a plurality of maxima, thus causing focusing characteristics of the AF to deteriorate.